1. Field of the Invention
The present invention relates to a method for manufacturing a reinforcing structure for tires of vehicles, comprising the following steps: preparing strip-like segments each comprising longitudinal filiform elements arranged mutually parallel at least partially coated by at least a layer of elastomeric material; applying the strip-like segments in mutually approached relationship along the circumferential development of the toroidal support, to form at least a reinforcing layer having continuous circumferential development about a geometric axis of rotation.
The invention further relates to an apparatus for implementing the aforementioned method, said apparatus being of the type comprising: a unit for the feeding of strip-like segments arranged mutually parallel at least partially coated by at least a layer of elastomeric material; a laying unit for applying each of said strip-like segments onto a toroidal support, according to a pre-set laying angle relative to a direction of circumferential development of the toroidal support itself, first angular actuation devices to determine a relative motion between the laying unit and the toroidal support, about a geometric axis of the toroidal support itself.
In the course of the present description, the invention shall be illustrated with particular reference to the manufacture of a belt structure of a tire. It is however hereby specified that the method and the apparatus according to the invention can be employed to manufacture a carcass structure of the tire or, more generally, any other reinforcing structure, comprising cords oriented in mutually parallel fashion and/or according to a pre-set angle relative to an equatorial plane of the tire.
2. Description of the Related Art
A tire for vehicle wheels normally comprises a carcass structure essentially composed by one or more carcass plies shaped according to a substantially toroidal configuration and presenting its axially opposite lateral edges engaged to respective annular reinforcing structures incorporating circumferentially inextensible inserts, usually called xe2x80x9cbead ringsxe2x80x9d. Each annular reinforcing structure is incorporated in a so-called xe2x80x9cbeadxe2x80x9d defined along an inner circumferential edge of the tire for the anchoring thereof to a corresponding mounting rim.
On the carcass structure is applied, in radially external position, a belt structure comprising one or more belt layers shaped in a closed loop, essentially composed by textile or metal cords suitably oriented relative to each other and relative to the cords belonging to the adjacent carcass plies.
In a position radially external to the belt structure is also applied a tread band, normally constituted by a strip of elastomeric material of adequate thickness. It should be specified that, for the purposes of the present description, the term xe2x80x9celastomeric materialxe2x80x9d means the rubber compound in its entirety, i.e. the set formed by at least a polymeric base suitably amalgamated with reinforcing fillers and/or process additives of various kinds.
On the opposite sides of the tire is applied a pair of sidewalls each of which covers a lateral portion of the tire lying between a so-called shoulder area, located in proximity to the corresponding lateral edge of the tread band, and the corresponding bead.
In the manufacturing processes of less recent design, each belt layer is formed by joining sequentially a plurality of segments obtained by cutting to measure a continuous strip composed by a plurality of parallel longitudinal cords incorporated in an elastomeric layer. More in particular, the cutting and joining operations are performed in such a way as to obtain a so-called belt ring, wherein the cords of each segment are oriented according to a predetermined inclination relative to the circumferential development of the ring itself and parallel to the cords of the contiguous segments.
The completed belt ring, which can also comprise two or more layers formed in succession in radial superposition relationship, is associated in radially external position to the carcass structure, normally simultaneously with an operative step wherein the latter, initially obtained in the form of a cylindrical sleeve, is shaped according to a toroidal configuration.
Recently, particular attention has been dedicated to the search for manufacturing methods which would allow to eliminate or at least limit the manufacture of intermediate semi-finished products required for the manufacture of the tires. For instance, in the European patent application EP 97830731.2, in the name of the same Applicant, a method for manufacturing tires is described wherein the carcass ply or plies, as well as each of the belt layers, are obtained by laying, one after the other in circumferential approach relationship, a plurality of strip-like segments onto a toroidal support shaped according to the internal conformation of the tire to be obtained.
Document WO 99/17920 describes a method and an apparatus for manufacturing a belt layer by the laying of strip-like segments cut off from a continuous strip-like element. Each segment, once cut off from the continuous strip-like element, is drawn by means of magnetic or suction-cup gripping organs, commanded by one or more robot arms. The gripping organs hold the strip-like segment in correspondence with its opposite extremities, and possibly in correspondence with its central section, and are actuated upon command from the robot arms to cause the application of the segment itself onto the exterior surface of a toroidal support, according to a predetermined angle relative to the circumferential development thereof. Once the application is complete, the toroidal support is made to rotate about its own geometric axis according to a predetermined angle, to allow the application of a new strip-like segment adjacently to the one applied previously. The sequential repetition of the steps described above causes the formation of a belt layer extending according to the entire circumferential development of the toroidal support.
The Applicant has however noted that the laying of strip-like segments carried out according to the teachings of the prior art does not bring about a perfect structural homogeneity in the reinforcing structure obtained thereby.
In accordance with the present invention, it has been found that it is possible to guarantee a perfect structural homogeneity to a belt layer or other reinforcing structure obtained by means of the sequential laying of strip-like segments, if during the laying of each segment a relative rotation is brought about between the toroidal support and the segment itself, about an axis of correction that is substantially radial to the geometric axis of the toroidal support.
In particular, the subject of the present invention is a method for manufacturing a reinforcing structure for tires of vehicles, characterised in that during the application of each of said strip-like segments between the strip-like segment itself and the toroidal support, a relative angular rotation is caused about an axis of correction substantially radial to said geometric axis of rotation.
More specifically, the angular rotation about the axis of correction is advantageously obtained in a progressive manner during the application of the strip-like segment.
According to a preferential embodiment of the invention, it is also provided for the angular rotation about the axis of correction to be controlled in such a way as to bring about the application of the segment according to an orthodromic trajectory relative to the exterior surface of the toroidal support.
In particular, said relative angular rotation is preferably carried out by the actuating of the toroidal support, about an axis laying in an equatorial plane of the toroidal support.
Preferably, the axis of correction about which said angular rotation is carried out is situated in barycentric position relative to the strip-like segment that is about to be applied onto the toroidal support.
It is also advantageously provided for the preparation of said strip-like segments to be effected by means of cutting actions sequentially executed on at least a continuous strip-like element incorporating said filiform elements in said layer of elastomeric material.
Advantageously, each cutting action is followed by the application of the individual segment thus obtained onto the toroidal support.
It is also preferably provided for the individual strip-like segments to be sequentially positioned on the toroidal support according to a circumferential distribution pitch corresponding to the width of the strip-like segments themselves, measured in correspondence with an equatorial plane of the toroidal support.
According to a preferential embodiment of the present invention, the application of each strip-like segment comprises the following steps: laying the strip-like segment transversely relative to an equatorial plane of the toroidal support; radially approaching the strip-like segment to the toroidal support; rotating the toroidal support according to an angular pitch corresponding to the circumferential distribution pitch of the strip-like segments.
Preferably, a further step is carried out whereby each strip-like segment is pressed against the toroidal support, said pressing being initially carried out in proximity with a central portion of the respective strip-like segment and subsequently extended towards the opposite extremities of the strip-like segment itself.
In a preferential embodiment, the pressing step is carried out simultaneously with said approaching step.
If need be, it may be advantageously provided for the toroidal support to be constituted by a previously formed carcass structure.
In a preferential embodiment, however, at least one step is provided whereby a carcass structure is manufactured on the toroidal support, said step entailing the application onto the toroidal support being cared out by laying each strip-like segment directly onto said carcass structure.
The invention also relates to an apparatus for manufacturing a reinforcing structure for tires of vehicles, characterised in that it further comprises second angular actuation devices able to be activated during the application of each strip-like segment to cause, between the strip-like segment itself and the toroidal support, a relative angular rotation about an axis of correction that is substantially radial to said geometric axis of rotation.
Advantageously, the second angular actuation devices are operatively interpolated with said laying unit to cause the application of the segment according to an orthodromic trajectory relative to the exterior surface of the toroidal support.
Preferably, said second actuating devices are mechanically connected to said toroidal support to rotate the latter angularly about said axis of correction
More in particular, said axis of correction lies substantially in an equatorial plane of the toroidal support.
In a preferential embodiment of the invention, said feeding unit comprises: a cutting organ operating on a continuous strip-like element to obtain therefrom said strip-like segments; a gripping organ movable between a first operative position wherein it engages a terminal end of said continuous strip-like element in proximity to the cutting organ, and a second operative position wherein it is removed from the cutting organ to extend the continuous strip-like element beyond the cutting organ itself, according to a segment whose length corresponds to that of the strip-like segment to be obtained.
Also in accordance with a preferential embodiment, said laying unit comprises at least a presser element movable in contrast relationship against the exterior surface of the toroidal support to cause the application of the strip-like segment.
More in detail, said laying unit comprises: at least two of said presser elements borne each by a respective support element, a guide structure bearing said support elements; radial actuation devices for translating the presser elements in radial approach to the exterior surface of the toroidal support; transverse actuation devices for translating the presser elements from a first operative condition wherein they are mutually approached to a second operative condition wherein they are removed relative to the equatorial plane of the toroidal support.
The presence may also be advantageously provided of auxiliary holding elements for holding the strip-like segment cut off by the action of said cutting organ.
Preferably, said auxiliary holding elements are movable relative to the presser elements in a direction substantially radial to the toroidal support.